A film device for preventing leakage and permeation in the inner cavity of a meal box

Abstract

This utility model provides a leak-proof and seepage-proof film covering device for the inner cavity of a lunch box, belonging to the technical field of film covering devices. The leak-proof and seepage-proof film covering device for the inner cavity of a lunch box includes: a box body with an annular rim extending horizontally inward around the box opening; an upper film, which is a continuous film covering the entire inner cavity of the box body; a lower film, which is a U-shaped frame, with the outer edge of the frame matching the size of the annular rim, and the inner edge of the frame located inside the edge of the box opening in the horizontal projection direction, the lower film being stacked below the upper film and attached to the upper surface of the annular rim; and a heat-sealing structure, in which the upper film and the lower film are heat-sealed at the annular rim in a staggered manner, the outer periphery of the upper film being heat-sealed to the outer ring area of ​​the annular rim, and the outer periphery of the lower film being heat-sealed to the inner ring area of ​​the annular rim, the inner ring area being closer to the center of the box opening than the outer ring area, thus solving the problem that the traditional single-layer sealing film of a lunch box fails completely once the edge is broken, and the lack of secondary protection leads to leakage of soup.

Description

Technical Field

[0001] This utility model belongs to the technical field of film coating devices, specifically, it relates to a film coating device for preventing leakage and seepage in the inner cavity of a lunch box. Background Technology

[0002] Modern food containers have become a core part of the food distribution process, from takeout delivery to pre-prepared meals. They must meet multiple requirements, including portability, low cost, airtightness, heat resistance, and leak prevention. Common food containers are often made of plastic or paper-plastic composite materials through one-piece injection molding, with a smooth rim and a single-layer film lining the inner cavity. The film's perimeter is bonded to the rim using heat pressing, forming a so-called "sealing film." This structure often performs well during factory testing, but its weaknesses gradually become apparent during subsequent transportation, handling, refrigeration, microwave heating, and repeated opening and closing by consumers. First, the film and the rigid container are made of different materials, resulting in significant differences in thermal expansion and contraction, making the edges prone to slight warping after temperature cycles. Second, the continuous vibration of delivery vehicles during operation causes the film surface to be in a high-frequency, slight bending state, leading to fatigue cracks initiating and propagating along the heat-sealing line. Third, when oily or savory dishes are microwaved, localized overheating causes oil to seep into the adhesive layer, resulting in a sharp drop in adhesion and the film edges being lifted by steam, creating "side leaks." If the seal fails, the soup will seep out through the gaps at the box opening, not only contaminating the outer packaging but also potentially scalding consumers and causing complaints. To alleviate these problems, the industry has tried thickening the single-layer film, using high-viscosity adhesive, or adding outer ring buckles. However, thickening the film leads to longer heat-sealing time and increased energy consumption, while high-viscosity adhesives tend to string at high temperatures. Buckle buckles increase costs due to the complexity of the molds. Moreover, these methods are all "single-point reinforcements" and fail to fundamentally solve the reliability bottleneck caused by "single film, single seal." They also do not provide redundant structural designs for secondary protection after the film breaks. Therefore, the market still expects a low-cost film coating solution that can achieve "leak-proof" even after breakage without the need for electronic equipment or expensive materials. Utility Model Content

[0003] In view of this, the present invention provides a leak-proof and seepage-proof film covering device for the inner cavity of a lunch box, which solves the problem that the traditional single-layer sealing film of a lunch box will fail as a whole once the edge is broken, and the lack of secondary protection will lead to the leakage of soup.

[0004] This utility model is implemented as follows:

[0005] This utility model provides a leak-proof and seepage-proof film covering device for the inner cavity of a lunch box, comprising:

[0006] The box body has an annular rim that surrounds the opening and extends horizontally inward;

[0007] The upper membrane is a continuous membrane that covers the entire inner cavity of the box, with its periphery overlapping the upper surface of the annular opening.

[0008] The lower membrane is a U-shaped frame. The outer edge of the frame matches the size of the annular opening. The inner edge of the frame is located inside the edge of the box opening in the horizontal projection direction. The lower membrane is stacked below the upper membrane and is attached to the upper surface of the annular opening.

[0009] The heat-sealing structure involves heat-sealing the upper and lower films at the annular opening edge in a staggered manner, forming a double-layer stepped sealing strip extending circumferentially along the box opening. The outer periphery of the upper film is heat-sealed to the outer ring area of ​​the annular opening edge, while the outer periphery of the lower film is heat-sealed to the inner ring area of ​​the annular opening edge. The inner ring area is closer to the center of the box opening than the outer ring area, causing the sealing tracks of the two films to be staggered in the horizontal direction.

[0010] The technical effects of the leak-proof and seepage-proof film covering device for the inner cavity of a lunch box provided by this utility model are as follows: The film covering device forms a double-layer stepped sealing strip that is horizontally staggered by heat sealing the upper intact film and the lower U-shaped frame film at the annular opening edge. Even if the upper film is torn, the liquid still needs to bypass the lower frame film to reach the outside of the box, thus naturally forming a redundant sealing path in the structure, significantly extending the leakage path, and achieving the accidental protection effect of "no leakage even if one layer is broken". Moreover, the entire sealing strip can be completed by only one heat sealing process, which is simple to manufacture and low in cost.

[0011] Based on the above technical solution, the leak-proof and seepage-proof film covering device for the inner cavity of the lunch box of this utility model can be further improved as follows:

[0012] The upper surface of the annular opening is provided with an outer ring boss and an inner ring boss. The outer ring boss is located at the outermost edge of the opening, and the inner ring boss is located inside the outer ring boss and is lower in height than the outer ring boss. The upper film is attached to the top surface of the outer ring boss, and the lower film is attached to the top surface of the inner ring boss. Due to the height difference of the bosses, the two films form a stepped cross-section after heat sealing.

[0013] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: After setting double protrusions with the outer side higher and the inner side lower on the upper surface of the annular opening, the two layers of film automatically form a stepped cross section due to the height difference. During heat sealing, the protrusions play a role in positioning and pressure concentration, which not only prevents the film layer from slipping but also produces a wedge-shaped pressing effect at the sealing interface, further enhancing the edge anti-warping ability and ensuring that the sealing strip will not delaminate due to friction during transportation or stacking.

[0014] Furthermore, the inner edge of the U-shaped frame of the lower membrane bends downward to form a skirt. The skirt is attached to the inner wall of the box opening and extends to the shoulder of the box. The skirt is fixed to the inner wall of the box opening with dotted hot melt adhesive, so that the lower membrane forms a secondary water-blocking ring on the inside of the box opening.

[0015] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the skirt extending downward from the inner edge of the lower membrane is attached to the inner wall of the box opening and fixed with adhesive, which can form a secondary water-blocking ring independent of the main sealing strip on the inner side of the box opening. When liquid seeps horizontally along the rupture of the upper membrane, the skirt directly intercepts and guides the liquid back into the box, achieving immediate protection of "seeping while blocking". At the same time, the skirt provides support to the side wall of the box opening, reducing the bending stress caused by the deformation of the box in the heat-sealing area.

[0016] Furthermore, the heat-sealing structure forms a continuous staggered heat-sealing line between the upper and lower films. This heat-sealing line includes an outer heat-sealing line and an inner heat-sealing line. The outer heat-sealing line fuses the upper film with the outer ring area along the annular opening, and the inner heat-sealing line fuses the lower film with the inner ring area along the annular opening. The two heat-sealing lines form concentric closed loops with different radii in the horizontal plane.

[0017] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the misaligned heat-sealing lines are designed as concentric closed rings with different radii, so that the sealing trajectories of the outer ring and the inner ring are independent of each other in the horizontal plane. If one ring fails due to a defect, the other ring will still remain intact. In addition, the radial interval between the two heat-sealing lines sets a forced bypass path for the liquid, which eliminates the risk of overall leakage caused by single-point failure from the mechanism and improves the sealing reliability.

[0018] Furthermore, an unsealed buffer zone is left between the outer heat-sealed line and the inner heat-sealed line. The upper and lower films at the buffer zone remain in a free state that can slide relative to each other, so as to absorb the film stress when the box body is deformed by heat.

[0019] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: by retaining an unsealed buffer zone between the two heat-sealed lines, the upper and lower membranes can slip slightly relative to each other when the box expands and contracts with heat. The buffer zone absorbs the stress of the membrane layer, thereby preventing the heat-sealed lines from being continuously stretched and cracked, and extending the sealing life. At the same time, the free membrane layer in the buffer zone can bulge slightly when under pressure, forming an elastic pad effect, which further prevents liquid from breaking through.

[0020] Furthermore, the upper membrane has an arc-shaped thinning area at the corner of the box opening. The membrane thickness of the thinning area is less than that of the surrounding area, so that the arc-shaped thinning area undergoes controllable local tensile deformation preferentially before the edge of the sealing strip, preventing tearing from extending to the area covered by the lower membrane.

[0021] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: After the upper membrane is set with an arc-shaped thinning zone at the corner of the box opening, when the membrane surface is stretched due to negative pressure inside the box or external force, the thinning zone will preferentially generate controllable stretching without breaking. Moreover, the arc-shaped structure will distribute the stress to a larger area, preventing cracks from extending in a straight line to the area covered by the lower membrane, thereby limiting potential damage to the "safety redundancy zone" and maintaining the overall leak-proof performance.

[0022] Furthermore, the lower membrane's U-shaped frame has outwardly protruding ears at its four corners. The ears extend horizontally to the outer side of the corner of the annular opening and are fixed together with the upper membrane by heat sealing, so that a reinforced sealing corner is formed at the corner by the overlapping of three membranes.

[0023] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the four corner ears of the lower membrane are heat-sealed together with the upper membrane to form a three-layer overlapping reinforced sealing corner. By utilizing the natural high stress concentration characteristics at the corner, the position most prone to warping is transformed into a multi-layer interlocking reinforcement point, so that the sealing corner remains in place when the box is dropped or subjected to lateral pressure, avoiding the common problem of traditional single membrane structures coming loose at the corner first.

[0024] Furthermore, the lower surface of the annular opening edge is provided with a groove that mates with the lid. The groove corresponds to the double-layer stepped sealing strip in the vertical direction. When the lid is closed, the inner wall of the groove simultaneously squeezes the heat-sealed edges of the upper and lower films, forming a double-sided clamping seal on the opening edge.

[0025] The beneficial effects of adopting the above-mentioned improved solution are as follows: the groove on the lower surface of the annular opening corresponds to the lid. When the lid is closed, the inner wall of the groove simultaneously squeezes the heat-sealed edges of the upper and lower films, forming a double clamping on both sides of the opening. The lid itself uses its locking force to press the sealing strip into a "closed" state, achieving secondary sealing without the need for additional adhesive strips. The clamping force is automatically released when the lid is opened, making it convenient to use and capable of repeated sealing.

[0026] Furthermore, an elastic mesh fiber layer is sandwiched between the upper and lower membranes. During the heat sealing process, the mesh fiber layer is partially pressed between the two membranes to form a mechanical interlock, thereby improving the peel strength of the two membranes in the misaligned heat sealing area.

[0027] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: after the elastic mesh fiber layer is partially pressed between the two membranes, a three-dimensional mechanical interlock is formed at the membrane interface, which significantly improves the peel strength. Even if the hot melt adhesive swells due to long-term contact with oily food, the mesh fiber still pulls the two membranes together like a "stitch", preventing the sealing tape from delaminating due to adhesive failure and maintaining the integrity of the redundant seal.

[0028] Furthermore, the inner edge of the U-shaped frame of the lower membrane is provided with an upwardly folded edge. After heat sealing, the folded edge is attached to the lower surface of the upper membrane, so that a U-shaped microcavity with an opening facing the center of the box is formed between the folded edge and the upper membrane. The U-shaped microcavity generates a capillary flow resistance effect when the liquid reaches the inner edge.

[0029] The beneficial effects of adopting the above-mentioned improved scheme are as follows: the folded edge of the inner edge of the lower membrane is folded upward and abuts against the lower surface of the upper membrane to form a U-shaped microcavity. When the liquid reaches the inner edge, the U-shaped cavity uses capillary force to generate an instantaneous blocking effect, so that the liquid is retained in the cavity under its own surface tension and does not continue to climb outward, achieving a self-sealing effect of "liquid stops as soon as it arrives". At the same time, the folded edge provides local support for the upper membrane, reducing the risk of concentrated leakage caused by membrane collapse.

[0030] Compared with existing technologies, the beneficial effects of the leak-proof and seepage-proof film covering device for the inner cavity of a lunchbox provided by this utility model are as follows: This utility model introduces the concept of "double-layer staggered heat sealing" between the existing lunchbox rim and the film covering. Through the stepped layout of the upper complete film and the lower U-shaped frame film, the original single-life sealing line is upgraded to a "outer ring-inner ring" double insurance. This ensures that even if liquid breaks through any single point, it still needs to bypass another complete film ring before leaking out, thus implanting a redundant sealing path at the structural level. Because the heat sealing trajectories of the two films are staggered in the horizontal plane, even if the outer heat sealing line has gaps due to vibration or grease corrosion, the inner heat sealing line still remains in contact with the box opening and continues to perform its sealing function, achieving "no leakage even if one layer is broken," significantly reducing the leakage rate in transportation and microwave scenarios. The staggered heat sealing also naturally forms a height difference and buffer gap between the two films. When the box expands and contracts with temperature, the film layer can slip slightly, and the stress is concentrated in the buffer zone rather than the heat sealing line, avoiding the instantaneous failure caused by the linear propagation of fatigue cracks in traditional structures. The skirt extending downwards from the inner edge of the lower membrane forms a second water-retaining ring on the inside of the box opening, guiding any seeping liquid back into the cavity and preventing it from continuing to creep outwards along the side walls. After the four corner flaps are heat-sealed together with the upper membrane, the traditionally warp-prone corners are transformed into three interlocking reinforcement points, ensuring the seal remains intact even in the event of a drop or lateral pressure. The groove on the lower surface of the opening corresponds to the lid; when closed, the inner wall of the lid's groove simultaneously presses against the edges of the double membranes, creating a double-sided clamping effect that compresses the seal into a "closed" state. This allows for repeated sealing without the need for additional adhesive strips, and the clamping force is automatically released when the lid is opened, providing a user experience identical to traditional single-membrane lunch boxes. An elastic mesh fiber layer forms a three-dimensional mechanical interlock at the interface of the two membranes. Even if prolonged contact with oily foods causes the hot melt adhesive to swell, the mesh fibers maintain the membrane bond like stitching, preventing the redundant seal from disintegrating due to adhesive failure. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1An example diagram showing the unfolded form of a leak-proof and seepage-proof film covering device for the inner cavity of a lunchbox;

[0033] Figure 2 A bottom view of an unfolded, leak-proof and seepage-proof film covering device for the inner cavity of a lunchbox;

[0034] Figure 3 An overall example diagram of a leak-proof and seepage-proof film covering device for the inner cavity of a lunch box;

[0035] The attached diagram lists the components represented by each number as follows:

[0036] 10. Box body; 11. Annular rim; 111. Outer ring boss; 112. Inner ring boss; 20. Upper film; 30. Lower film. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings.

[0038] like Figures 1-3 The image shown is an example diagram of a leak-proof and seepage-proof film covering device for the inner cavity of a lunchbox provided by this utility model, comprising:

[0039] The box body 10 has an annular rim 11 that surrounds the opening of the box and extends horizontally inward;

[0040] The upper membrane 20 is a continuous membrane that covers the entire inner cavity of the box 10, and its periphery overlaps the upper surface of the annular opening 11.

[0041] The lower membrane 30 is a U-shaped frame. The outer edge of the frame matches the size of the annular opening 11. The inner edge of the frame is located inside the edge of the box opening in the horizontal projection direction. The lower membrane 30 is stacked below the upper membrane 20 and is attached to the upper surface of the annular opening 11.

[0042] The heat-sealing structure involves heat-sealing the upper film 20 and the lower film 30 at the annular opening edge 11 in a staggered manner, forming a double-layer stepped sealing strip extending circumferentially along the box opening. The outer periphery of the upper film 20 is heat-sealed to the outer ring area of ​​the annular opening edge 11, and the outer periphery of the lower film 30 is heat-sealed to the inner ring area of ​​the annular opening edge 11. The inner ring area is closer to the center of the box opening than the outer ring area, so that the sealing tracks of the two films are staggered in the horizontal direction.

[0043] In the above technical solution, the upper surface of the annular rim 11 is provided with an outer ring boss 111 and an inner ring boss 112. The outer ring boss 111 is located at the outermost edge of the rim, and the inner ring boss 112 is located inside the outer ring boss 111 and is lower in height than the outer ring boss 111. The upper film is attached to the top surface of the outer ring boss 111, and the lower film is attached to the top surface of the inner ring boss 112. The two films form a stepped cross section after heat sealing due to the height difference of the bosses.

[0044] Furthermore, in the above technical solution, the inner edge of the U-shaped frame of the lower membrane 30 bends downward to form a skirt. The skirt is attached to the inner wall of the box opening and extends to the shoulder of the box body 10. The skirt is fixed to the inner wall of the box opening with dotted hot melt adhesive, so that the lower membrane forms a secondary water-blocking ring on the inner side of the box opening.

[0045] Furthermore, in the above technical solution, the heat-sealing structure forms a continuous staggered heat-sealing line between the upper film 20 and the lower film 30. The heat-sealing line includes an outer heat-sealing line and an inner heat-sealing line. The outer heat-sealing line fuses the upper film with the outer ring area of ​​the annular opening 11, and the inner heat-sealing line fuses the lower film with the inner ring area of ​​the annular opening 11. The two heat-sealing lines form concentric closed loops with different radii in the horizontal plane.

[0046] Furthermore, in the above technical solution, an unsealed buffer zone is left between the outer heat-sealed line and the inner heat-sealed line. The upper and lower films at the buffer zone are kept in a free state that can slide relative to each other, so as to absorb the film stress when the box 10 is deformed by heat.

[0047] Furthermore, in the above technical solution, the upper membrane 20 has an arc-shaped thinning area at the corner of the box opening. The membrane thickness of the thinning area is less than that of the surrounding area, so that the arc-shaped thinning area undergoes controllable local tensile deformation preferentially before the edge of the sealing strip, preventing tearing from extending to the area covered by the lower membrane.

[0048] Furthermore, in the above technical solution, the lower membrane 30 has outwardly protruding ears at the four corners of its U-shaped frame. The ears extend horizontally to the outside of the corner of the annular opening 11 and are fixed together with the upper membrane by heat sealing, so that a reinforced sealing corner with three overlapping membranes is formed at the corner.

[0049] Furthermore, in the above technical solution, the lower surface of the annular opening 11 is provided with a groove that mates with the lid. The groove corresponds to the double-layer stepped sealing strip in the vertical direction. When the lid is closed, the inner wall of the groove simultaneously squeezes the heat-sealed edges of the upper and lower films to form a double-sided clamping seal on the opening.

[0050] Furthermore, in the above technical solution, an elastic mesh fiber layer is sandwiched between the upper membrane 20 and the lower membrane 30. During the heat sealing process, the mesh fiber layer is partially pressed between the two membranes to form a mechanical interlock, thereby improving the peel strength of the two membranes in the misaligned heat sealing area.

[0051] Furthermore, in the above technical solution, the inner edge of the U-shaped frame of the lower membrane 30 is provided with an upward folded edge. After heat sealing, the folded edge is attached to the lower surface of the upper membrane, so that a U-shaped microcavity with an opening facing the center of the box is formed between the folded edge and the upper membrane. When the liquid reaches the inner edge of the U-shaped microcavity, a capillary flow resistance effect is generated.

[0052] Specific Implementation Example 1: The box body is a disposable polypropylene thin-walled rectangular lunch box. The opening extends horizontally outward to form a ring. An outer ring boss and an inner ring boss are molded on the upper surface of the ring. The top surface width of the outer ring boss is slightly larger than that of the inner ring boss, and it is approximately twice the wall thickness of the inner ring boss. The upper film is a single sheet of microwaveable polyester composite film, covering the entire inner cavity and resting on the top surface of the outer ring boss. The lower film is cut into a U-shaped frame, with its outer edge aligned with the inner edge of the outer ring boss, and a small gap left between its inner edge and the side wall of the box opening. The frame naturally sits on the top surface of the inner ring boss. The hot-pressing mold has two independent heating blades. The outer heating blade presses the upper film and the outer ring boss together, while the inner heating blade presses the lower film and the inner ring boss together. The two blades are staggered in the horizontal radius direction, forming a double-layer stepped sealing strip. After heat sealing, the inner edge of the lower film continues to bend downward to form a skirt. The skirt is attached to the inner side wall of the box opening and positioned with food-grade dotted hot melt adhesive, forming a second water-blocking ring. The lid has raised ribs around its perimeter that match the groove on the rim. When the lid is closed, the raised ribs embed into the grooves, clamping the sealing strip tightly from top to bottom. This embodiment is suitable for Chinese takeout scenarios involving rich broth. Even if the upper film is punctured by chopsticks or the edges are slightly warped due to microwave heat, the broth must bypass the inner heat-sealing line and be blocked by the skirt, ensuring "no leakage even when broken," and the outer packaging remains dry when it reaches the consumer.

[0053] Specific Embodiment Two: The box body adopts a circular paper-plastic hybrid deep bowl, with the rim horizontally expanding outward into a wide ring. The upper surface of the ring has no raised or recessed protrusions, only a shallow groove is die-cut on the inner side as an inner ring positioning mark. The upper film is a circular full-coverage film with a diameter slightly larger than the outer diameter of the rim; the lower film is still a U-shaped frame, but the frame width is reduced by about half compared to Embodiment One, and the inner edge is folded upward to form a short folded edge. During hot pressing, intermittent low-temperature hot melt adhesive is first rolled onto the back of the outer ring of the lower film and pasted onto the inner side of the shallow groove of the rim to complete the "pre-positioning"; then the upper film is covered, and a single-ring wide-blade hot press head is used to press it together in one go. Since the depth of the shallow groove is only equivalent to the film thickness, the adhesive dots remelt at high temperature, so that the upper film and the outer ring of the rim, and the lower film and the inner side of the shallow groove are completed in the same process with staggered heat sealing, forming a concealed double-layer seal. The folded edge adheres to the lower surface of the upper film to form a U-shaped microcavity. The lid is a transparent PET snap-on lid with no internal ribs; it relies solely on the elasticity of the lid wall to hold the opening edge tightly, generating circumferential pressure on the sealing strip. This embodiment is suitable for cold chain scenarios such as light meal salads and fruit cups. During repeated opening and closing of the refrigerator in a shopping mall and when consumers take food, if the upper film is accidentally torn by a fork, the U-shaped microcavity uses capillary force to trap the juice, while the narrow-framed lower film continues to adhere to the shallow groove, preventing juice from flowing out along the wall and keeping the refrigerator shelf clean. The entire box can also be used directly as a display container without the need for additional labeling or covering.

[0054] Specifically, the principle of this invention is as follows: This invention utilizes a double-membrane layout of "horizontal misalignment + vertical stacking" to construct a stepped double-sealing interface in the box opening area. During hot pressing, the outer periphery of the upper membrane is fused with the outer ring of the opening edge to form the first sealing ring; the outer periphery of the lower U-shaped frame membrane is fused with the inner ring of the opening edge to form the second sealing ring. The two rings are staggered in the horizontal radial direction, forming a "parallel" rather than "series" sealing topology. If the liquid breaks through the first ring, it must cross the buffer zone laterally and traverse the second ring to leak out. This detour significantly prolongs the leakage path, and the liquid loses energy due to surface tension and viscous resistance when crossing, weakening the permeation force layer by layer, thus achieving a "break-without-leaking" redundancy effect. In the vertical direction, the outer ring protrusion is higher than the inner ring protrusion. After heat sealing, the two membranes naturally form a stepped cross-section. The steps not only serve a positioning function but also generate a wedge-shaped self-locking under pressure, becoming tighter with increasing pressure, preventing the membrane edge from being pushed up by steam or external force. The unsealed buffer zone between the two membrane layers allows for slight slippage of the membrane layers under temperature differences or mechanical vibrations. Stress is released through the buffer zone, preventing cracking caused by concentrated stress in traditional continuous heat-sealed lines. The skirt of the lower membrane's inner edge is folded down and fixed to the inner wall of the box opening with adhesive. Utilizing the "wall adhesion" effect, a vertical barrier is formed in the lateral liquid permeation path. This barrier forms a 90-degree angle with the main sealing ring, requiring the liquid to change its flow direction to continue, further consuming permeation kinetic energy. The four corner ears transform the traditional high-stress corners into multi-layered, thickened areas. External forces are dispersed and blunted when they encounter the tearing wave front generated at the corners, making it difficult for cracks to penetrate the entire sealing ring. When the box lid is closed, the groove along the opening and the rib of the lid form opposing clamping surfaces, simultaneously pressing the edges of the double membrane layers to the upper and lower sides. The clamping force is perpendicular to the membrane surface, causing "secondary plastic flow" in the heat-sealed area. Micro-protrusions embed into the membrane surface, forming a micro-mechanical interlock, enhancing the tightness of the seal. The elastic mesh fiber layer partially melts into the surface of the two membranes under hot pressing and high temperature. After cooling, it forms a three-dimensional "seam" structure. When the adhesive layer loses its adhesiveness due to the swelling of grease, the mesh fiber still maintains the inter-membrane shear strength through bridging, ensuring that the redundant seal does not fail within its life cycle.

Claims

1. A film coating device for preventing leakage and permeation in the inner cavity of a meal box, characterized in that, include: The box body has an annular rim that surrounds the opening and extends horizontally inward; The upper membrane is a continuous membrane that covers the entire inner cavity of the box, with its periphery overlapping the upper surface of the annular opening. The lower membrane is a U-shaped frame. The outer edge of the frame matches the size of the annular opening. The inner edge of the frame is located inside the edge of the box opening in the horizontal projection direction. The lower membrane is stacked below the upper membrane and is attached to the upper surface of the annular opening. The heat-sealing structure involves heat-sealing the upper and lower films at the annular opening edge in a staggered manner, forming a double-layer stepped sealing strip extending circumferentially along the box opening. The outer periphery of the upper film is heat-sealed to the outer ring area of ​​the annular opening edge, while the outer periphery of the lower film is heat-sealed to the inner ring area of ​​the annular opening edge. The inner ring area is closer to the center of the box opening than the outer ring area, causing the sealing tracks of the two films to be staggered in the horizontal direction.

2. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 1, characterized in that, The upper surface of the annular rim is provided with an outer ring boss and an inner ring boss. The outer ring boss is located at the outermost edge of the rim, and the inner ring boss is located inside the outer ring boss and is lower in height than the outer ring boss. The upper film is attached to the top surface of the outer ring boss, and the lower film is attached to the top surface of the inner ring boss. Due to the height difference of the bosses, the two films form a stepped cross-section after heat sealing.

3. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 2, characterized in that, The inner edge of the U-shaped frame of the lower membrane bends downward to form a skirt. The skirt is attached to the inner wall of the box opening and extends to the shoulder of the box. The skirt is fixed to the inner wall of the box opening with dotted hot melt adhesive, so that the lower membrane forms a secondary water-blocking ring on the inside of the box opening.

4. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 3, characterized in that, The heat-sealing structure forms a continuous staggered heat-sealing line between the upper and lower films. The heat-sealing line includes an outer heat-sealing line and an inner heat-sealing line. The outer heat-sealing line fuses the upper film with the outer ring area along the annular opening, and the inner heat-sealing line fuses the lower film with the inner ring area along the annular opening. The two heat-sealing lines form concentric closed loops with different radii in the horizontal plane.

5. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 4, characterized in that, There is an unsealed buffer zone between the outer heat-sealed line and the inner heat-sealed line. The upper and lower films at the buffer zone are in a free state that can slide relative to each other, so as to absorb the film stress when the box is deformed by heat.

6. The film-coating device for preventing leakage and seepage inside a lunchbox according to claim 5, characterized in that, The upper membrane has an arc-shaped thinning area at the corner of the box opening. The membrane thickness of the thinning area is less than that of the surrounding area, so that the arc-shaped thinning area undergoes controllable local tensile deformation preferentially before the edge of the sealing strip, preventing tearing from extending to the area covered by the lower membrane.

7. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 6, characterized in that, The lower membrane has outwardly protruding ears at the four corners of its U-shaped frame. The ears extend horizontally to the outside of the corner of the annular opening and are fixed together with the upper membrane by heat sealing, so that a reinforced sealing corner with three overlapping membranes is formed at the corner.

8. A film-coating device for preventing leakage and seepage inside a lunchbox according to claim 7, characterized in that, The lower surface of the annular opening is provided with a groove that mates with the lid. The groove corresponds to the double-layer stepped sealing strip in the vertical direction. When the lid is closed, the inner wall of the groove simultaneously squeezes the heat-sealed edges of the upper and lower films, forming a double-sided clamping seal on the opening.

9. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 8, characterized in that, An elastic mesh fiber layer is sandwiched between the upper and lower membranes. During the heat sealing process, the mesh fiber layer is partially pressed between the two membranes to form a mechanical interlock, thereby improving the peel strength of the two membranes in the misaligned heat sealing area.

10. The film device for preventing leakage and permeation in the inner cavity of a meal box according to claim 9, characterized in that, The inner edge of the U-shaped frame of the lower membrane is provided with an upward folded edge. After heat sealing, the folded edge is attached to the lower surface of the upper membrane, so that a U-shaped microcavity with an opening facing the center of the box is formed between the folded edge and the upper membrane. The U-shaped microcavity generates a capillary flow resistance effect when the liquid reaches the inner edge.

Images